Electron tube circuit



Feb. 2,3, 1932. i F. E. TERMAN 1,846,043

ELEGTRON TUBE cRcUI'l.1A

Filed Nov. '7, 1929 5 Sheets-Sheet 1 IN V EN TOR.

BY w ATTORNEY Feb, 23, 1932. F. E. TERMAN 1,846,043

ELECTRON TUBE QIRCUIT l Filed Nov. 7, 1929 3 sheets-sheet 2 gade/2M Za gamma/w A TTORNEY f.

Feb. 23, 1932. F. E. 'flair-uuml 1,846,043

ELECTRON TUBE oIRcUT Filed NOV. '7, 1929 3 Sheets-Sheet 3 BY 7U/ i w 'ATTORNEY- Patented Feb. 23, 1932 FREDERICK E. TERMAN, OF STANFORD NVEI r Fries carrnonnre, asistencia T0 WIRED RADIO, INC., 0F NEW YORK, N. Y., CGEPQRATN 0F DEliAWARE nnnornoir rusa orncnlr Application led November 7, 1929. Serial No. 405,363.

My invention relates broadly to electron tube circuits and more particularly to an inverted 'vacuum tube systen'i.

@ne ot the objectsot my invention is to provide an electron tube circuit operating as a voltage reducing power ainpliier.

.'inother object oi' my invention is to provide an arrangement of elect-ron tube circuit in which voltage applied tothe input system may be reduced and delivered to the output system and in which a smaller voltage exists in the output system, according to a ratio dependent upon the amplilication constant of the tube.

vide an arrangement of electron tube circuit having the characteristic or voltage stepdown as distinguished trom a system in which the voltage amplitude is increased in successive stages. i

My invention has various applications where the problem arises ot reducing a high voltage to a smaller potential which will follow all oi' the voltage variations 'which t are impressed thereon. The circuit arrange nient of my invention is particularly adapted as au oscillograph or as a power transformer in a power distribution system where it is necessary to reduce potentials ci hundreds i oi thousands ot volts to relatively small voltages for distribution to circuitsv tor domestic or commercial consumption.

The circuit arrangement oi my invention is applicable in oscillator systems, frequency control systems, in circuits tor measuring voltage, in rectifier circuits, in circuits employing multiple electron tubes and in nu mer-ous other instances, as will be more it'ully` understood from the specification hereinafter following by reference to the accompanying drawings in which:

liiglu'e l diagrammatically illustrates the c'lemciital circuit arrangement for the electron tube system of my invention; Fig. 2 illustrates characteristic curves showing the relationship between plate voltage and grid current at constant grid voltage in two standard types of electron tube; Fig.` 8 shows characteristic curves illustrating the relationship between grid current and grid volt` age at constant plate voltage in two standard type tubes arranged in thecircuit of my invention5` lig. d illustrates characteristic cru-ves `ior the types of tubes on which measurements illustrated in Figs. 2 and 3 were triton and showing the effects of saturation; liig. 5 shows aiset ot curves illustrating the relation ot plate and grid voltages required tor constant grid current in the circuit of my inveirticn; W illustrates the` static characteristic ot he vacuum tube circuit of my invention; llig. i' is a theoretical diagram lor more clearly explaining the operation of the circuit` oi my invention; Fig. 8 shows one i further obl|ect of my invention is to pro-` arrangement of circuit which I have employed for measuring the step-down ratio obtainable in the vacuum tube circuit of my invention; lltigxl shows a circuitwhich I have employed for measuring the dynamic grid resistance oi: the :inverted vacuum tube; Fig. l0 shows a circuit for measuring the relier: mutual conductance of the inverted vacuum tube; Fig. l shows characteristic curves :for two standard forms of tube showing the step-down ratio in the tube circuit of my invention; and. 12 illustrates in graphic `torni the dynamic grid resistance` tor tubes operated in accordance with my invention. i r l The basic circuit ot the system of my invention is shown in llig. l. rllie essential features o'this circuit are: L. the grid is o erated at a positive potential and so draws considerable current; `(2) the plate is operated at a negative potential and so draws no current; an d the input circuit is the plate` circuit, while the output circuit is the grid circuit. ln Fig. l the electron tube lis shown including a `catlmdc 2, a grid 3 and a plate it. The input circuit is shown at 5 connected between plate /l-and cathode 2 through battery systeinti. :The negative side of battery system G connects to the input circuit. The output circuit is indicated at -7 disposed in seriesA with the grid 3 and the cathode 2 with battery system 8 disposed therein, the positive terminal oit the battery` system 8 being con-` nected `to theinput circuit. `The cathode 2 is heated by battery 9, which may besutably contr-lledby resistor l0.

The vacuum tube in the circuit of my invention acts as a voltage reducer, or voltage this input voltage controls an appreciable grid current, thus-controlling considerable cn-V ergy inthe grid, or output, circuit.

The' operation of the Vacuu-m tube circuitV of4 my invention-v can best be visualized in terms of curves giving' the relation between grid current and plate and grid'y voltages. A completeset of such curves for twofrepresentati'vetubesis givenin Figs. 2', 3', 4', 5, and 6. O'neofithescv tubes has a u of about 3- (stepf d'ownratio of' approximately 3)" while thev other has a a of about 30 (step down ratio of approximately 30. As the two companion setsot curves are plottedto the same scales, and apply to tubes very similar toeach other in general construction except for the value oi? n, the effect of changing' theV step-down ratio'can be readily visualized.

The charts on' the lett in Figs. 2, 3, 4, 5, 1l andv 1:2 arel allprepared by an investigation of' the type ci?V tubey known as CX-S 1. The charts' on the right in the above figures were a-lP prepared by` investigating the character-- istics of thel tube known as IDG-240. All potentialsl in the figures arej measured with respect totheV negative filament lead.V

Thecurves of Fig. 2: show' thev relation be-y tween grid current and negative-plate voltage .tor various values of positivel grid; voltage. The results are seen to have a form similar to the i Fig-Ip (grid-voltageplate current) curvesoffthe usual vacuum-tube circuit; An important feature is that each curve in Fig. 2 has a straight line portion of more or less length. Variations of plate voltages within he boundaries of this straight line portion give rise to variations in gridcurrent that i extend. greatly the range of'plate voltage over which the grid current is proportional to changesin plate potential;

Fig. 3 gives the same information as FiggQv but in another form. The curves of Fig. 3 correspond to the usual Ep-Ip curves of the vacuum tube, and have the same form. The effects of limited electron emission from the filament are shown in Fig. 4. It is seen that as long as the filament temperature issuiicient to emit a small surplus above the number of electrons flowing to the positive grid, the filament temperature is unimportant.. yPortions of the curves'in Fig; 4 where the electron emission is insu'iiicient to' furnish the necessary supply of electrons required for normal operation are flattened out as the figure indicates. The departure from normal takes place at lower and lower grid currents as the filament voltage is reduced because the electron emission'dropslrapidly with reductionlin filament heating. i n j The curves in Fig. 5f are very important in theA theory of operationofl'thev vacuum tube circuitAA of my invention as will be eX'-` plained hereinafter.-

Fig. (iA differs from Fig. 2 only inE showing the eiect on the grid current oimakinfg the platevol-tagepositive. lt is seen that as soon as the plate begins to tale current, the grid circuitis robbed ot, alarge part of' its cur-- rent. The very sudden change of curvatureY in thecharacteristics at zero-plate voltsind-i- Cates that this-point gives a large rectifying etlect.'

The theory ofthe vacuum tubefcircuit ot my grid depends upon the electrostatic"iield'existingbetween iilainentfand grid,l and is subst-anshown'fromthe' theory ot electrostatics; that the' actual field is'V proportional vto the quan"-v t'ity (Egl-E/m)=, where Eg and Ep are the potentialsof the gridl and platen respectively',

and m isL a constant that is determined by the geometrical proportions of the tube and isl` notY aiiectcdby the electrode potentials.

Stating that the ieldl intensity between grid and filament is" proportional" to the quantity (Eg-FE 1,/m) is equivalent-to saying that 'Eg vlts= applied to the' grid' produce the same' field intensity as is produced by the applica' Theconstant tion of'mE;g volts onlthe plate; mv isf usu'a'lly larger than unity, rangingcommonly-'from-to-ffO.' The constant m is-larger' than. un-itybecause the' grid is so constructed and located that it is in abetter position to` produce; a high field intensity between. fila mentA and grid than is the plate.

' The' grid currentr is determi-ned by th'ej field'v intensity'Y between filament andi grid, and: this -iield is 'proportional' to the' quantity' I `or'const`antgrid current it (Est/M1 follows that (Eg-tETD/mi)A must'. be` constant.

Fig; v showsv a= seriesi off4 curves fon Vdifferent` constant values" of? gridl current.` TheseA "T invention rests upon'- thel fundamentalV tact that the current Howing. tothe positive curves are practically straight lines that are substantially parallel. The equation of a straight line in Fig. 5 is: r

(Eg -l-Ep/m) i constant that makes lm. a geometrical constant of the tube independent of electrode voltages, and that makes the grid current depend only `on the value of the quantity (Eg +En/m).

The constant m is the same as the constant ,i of the usual vacuum-tube circuit. Tests show that when the tube is used in the cirnl@ in plate potential `will have an effecten the grid current equivalent to the eifect of adding AED/fm. volts in the grid circuit. It follows from this that the elfect on the grid circuit of an input voltage es in Fig. l is Y exactly the same as though this input voltage had been replaced by a fictitious generator of 'voltage cS/m acting in the grid or outputk circuit.

rlibe equivalent circuit of the vacuum tube system of my invention is given in Fig. 7. The effect of a signal voltage eS applied to the input (plate) circuit is as though a gencrater having a voltage eS/m was inserted between the grid and filament ofthe tube. The minus sign is present because of the direction in which this voltage is assumed to act in Fig. 7 Which is the most convenient direction. The resistance Rg is the dynamic grid resistance, i. e. Rg is the resistance the grid circuit offers to an increment of voltage such as eS/m. It is the A. C. resistance of the grid circuit, and is analogous to the dynamic plate resistance Rp of the usual tube circuit. The value of Rg depends on the grid aud platebattery potentials, and can be deterniined by methods hereinafter explained. The voltage es that is ap lied to the input will generally be an A. voltage of magnitude E., and frequency f. This voltage superimposed on the negative plate battery potential by being introduced at the point marked InputHnFig 1,is equivalentto a voltage of amplitude *ES/mi and of frequency f acting in the equivalent circuit. The

current that this equivalent voltage produces depends upon the impedance of the equivalent circuit. This circuit consists of the dynamic grid resistance Rg in series With Whatever impedance is inserted in the grid circuit at the point marked Output in Fig.-1.` `The grid current produced as a result of apply ing the A. C. input voltage `of es==Es sin at` isthen i i i SES/m) sin wt p A. C. gridcurrent: Ra Z Where Z is the output impedance inserted in the grid circuit. y .Y

An important property of the vacuum tube circuit of my invention is the amount of change of grid current obtained with a given change of plate voltage, and with no load or y output impedance present'in the grid circuit.

The constant expressing this property is the ratio ZIK/(ZEP, and `can be called the reflex mutual conductance of the vacuum tube circuit of my invention and given th-e symbol g. The reflex mutual conductance of the vacuum tube of my invention is analogous in all its properties to the mutual conductance gm of the usual vaciu11ntube circuit. `In terms of fm. and Rg the reflex mutual conductance is g1. Z/m Rg When there is no load impedance inserted in the grid :circuit the application of a small voltage E to the plate circuit causes a change of grid current of fl The voltage stepdovvn ratio m ofthe vacuum tubecircuit of my invention can be measured by means of the bridge circuit shown in y F ig. 8. The electron tube l, as shown in Fig.

8, has its electrodes connected similar to the circuit in Fig. l, with the input circuit closed through resistance R1 and the output circuit Y completed through high potential battery 8, telephones 12 and resistance Rt. Rl `and R2 may serve as two arms of the grid circuit across which high frequency oscillations, such as oscillations of 1,000 cycles, are impressed.

When no'sound is heard in the telephones, an elementary application of the theory of the vacuum tube circuit of my inventionshovvs the resistances R1 and R2 must be such that sirable.

lili) The dy'fnamic grid ,resistanee'nRg' can:` be measured by ,theuse of analternating. current bridge, as shownin Fig. 9; The electron-tube 1 has its output circuit connected at X inone arm ofthe bridge. The other armsot the bridge are shown at 14, V and 16.with telephones. 18 connected across the arms. High frequency energy of, for example,.1,000 cycles is impressed across arms- 15-16. The meth- I od consists in making .the grid: filament resistance the X arm of the bridge. TheA grid potential to which the measurements apply is the battery voltage minus thevoltage drop in the bridge of the grid current. By'proper arrangement of bridoe resistances the correction'can be kept small. l

The reflexmutual conductance gVr of the vacuum tubey of my invention can be measured by the circuit shown in Fig.V 10. The

vacuum-tube 1 may have its input and output.v circuits associated substantially as illustrated.

in Fig. 8, wherein the input and output circuits are coupled through resistances R1 and R2. 'Ihe telephones 19vare connected between a point in the output circuit and the resistance R3. The impressed energy is supplied across resistance R3 and a point in the input circuit. Vhen the resistances arev such as to give no sound in thetelephones, an elementary application of the vacuum tube according to my inve-ntion shows that i grZRe/R1R2 Any one ofthe three resistances may be var. ried, although R3v isv generally most satisfactory for the variable element. Suitable values are R1= 100 ohms, R2: 1000 ohms, and R3 variable up to 100 ohms in tenth ohm steps.

Correction for the voltage drop inl R1 due to grid current must be made'to get the grid voltage from the battery potential.

In all of these measurements it is desirable to make the A. C. input voltage to the measuring equipment small. With large inputs there is some second harmonic current generated, Whi'ch masks the fundamentaly tone for which the bridge is to be balanced'. A microphone hummer is a suitable sourceof'audiofrequency Venergy. for the measurements.

The constants of the vacuum tube circuit of my invention can also be derived from the static curves by methods: analogous to those applied to static curves of ordinary vacuum tubes. The constants can also be determined by adding voltage increments in to the proper batteries, and-reading the results on meters'.

Results of measurements of m, and Rg for a low and a high ,a tube aregiven in Figs.. 11`

and 12. Examination of Fig. 11 shows that the voltage Ystep-down ratio m is subject to Y Tests of considerable fluctuations in value. a large number of'tubes under different conditions indicate that` the step-down: ratio fm, varies in anerratic manner when the grid ri. current is large, and particularly when: the

negative plate voltage is small.- For large negative potentials on the plate, andi where the grid current is relatively small', the; stepdown ratio m is practically constant at a value approximately equal to the ,t of the tube.

The dynamic grid resistance of the vacuum tube circuitv of my invention is rather low, even for veryjlow gridvoltages. This-is because of they proximity of the grid and filament instandardtubes. Forl ordinary receiving tubes, resistances inthe orderv of 1000 ohms are found for grid potentialsof. around volts.- The. dimensions4 of` the grid are not soy very.y important, for Fig. 12 shows that two tubes withl very ldifferent grid constructions have grid resistancesin the same order of magnitude.

Arsfheretofore noted-the voltage, reducing characteristic of the, electron tube circuit of my invention renders the circuitv particularly applicable. in power transmission and distribution systems where the electron tube has Vits input circuit.; connected to high, voltage lines, with its' `outputv circuit, connected to the V low voltage distribution lines operating asv a.

power: transformer.

The circuitv arrangement is particularly useful for the operation of anoscillogra-ph where it is'desired toprevent consumption ofcurrent, in themeasuring device. The circuit arrangement of-my inventionis ideally suited for.: this purpose. The voltage wave to be photographed is applied. directly to the plate using suitable plate bias battery. By the reducing action of the tube `this high voltage is Y transformed into a smallerpotential acting in the low impedance grid circuit, developing current variations that can be registered by the oscillograph.- ,f l

I also employ the circuit of my invention as aconstant frequency oscillator and as circuits for operating measuring instruments, such as a voltmeter. The circuit arrangement of my invention is also applicable for detection and rectification in signal receiving cir- The principles of my invention make the circuit highly desirable for numerous applications, and I have accordingly described my invention broadlyand desire that it be understood thatv the circuit thereof'rmay be used vIn an electron :tube circuit,Y a` thermionic. tube includingacathode, a gridand an -anode,:

described vthe preferred emtil] an input circuit comprising a source of potential disposed between said anode and cathode, an output circuit including a sec ond source of potential and disposed between said grid and cathode, said source of potential in said input circuit being connected to subject said anode to a negative Charge and said source of potential in said output circuit being adapted to subject said grid to a positive chai-ge.

In testimony whereof I aiX my signature.

FREDERICK E. TERMAN. 

